This invention relates to Fischer-Tropsch reactions for the production of hydrocarbons and a catalyst composition used in the process.
The art is replete with examples of Fischer-Tropsch catalytic processes for making hydrocarbons from H.sub.2 /CO mixtures. These processes yield olefinic, aromatic and paraffinic hydrocarbons as well as oxygenated hydrocarbons. Much of this art concerns itself with methods for improving conversion (i.e., the amount of carbon monoxide converted to the above-mentioned products), or methods for improving selectivity (i.e., the amount of carbon converted to a given desired product divided by the total carbon converted).
Many examples in the art relate to improvements in the selectivity to a desirable product such as ethylene or materials which can be thermally cracked to ethylene. Materials which can be thermally cracked to ethylene include C.sub.2 -C.sub.4 paraffinic hydrocarbons and C.sub.3 -C.sub.4 olefinic hydrocarbons. It is desirable to maximize the yield of ethylene in this process sub-group because losses occur when thermally cracking the other hydrocarbons to ethylene.
An example of such a process is U.S. Pat. No. 4,151,190 which discloses a method for increasing the selectivity to hydrocarbons containing 2 to 4 carbon atoms by the use of a 3-component catalyst comprising at least one material selected from the group consisting of a metal oxide or sulfide of molybdenum, tungsten, rhenium, ruthenium and platinum; at least one material selected from the group consisting of the hydroxides, oxides and salts of the alkali metals, alkaline earth metals, and thorium; and a support comprising alumina, silica, carbon, zirconia, magnesia, etc.
Another example is U.S. Pat. No. 4,199,522 which discloses a method for increasing the selectivity to C.sub.2 -C.sub.4 olefins by using a catalyst with less than 100 m.sup.2 /gm surface area and comprising at least one member of the group of metals, oxides or sulfides of molybdenum, tungsten, rhenium, ruthenium, nickel, palladium, rhodium, osmium, iridium, and platinum; and at least one member of the group of hydroxides, oxides or salts of alkali and alkaline earth metals; which catalyst may optionally be on a support comprising alumina, carbon, silica, zirconia, zircon, titanium dioxide, magnesia or mixtures thereof.
As good as these catalysts are, there is always room for improvement. It is an object of this invention to produce a Fischer-Tropsch catalyst composition which, when used in a Fischer-Tropsch process, is more selective to C.sub.2 -C.sub.4 olefins and particularly to ethylene. It is an object of this invention to provide a process with improved yields of C.sub.2 -C.sub.4 olefins and particularly ethylene in a Fischer-Tropsch process. While these objects are generally intended, it is not necessary for each and every possible embodiment of the invention to satisfy each of these criteria in order to be within the scope of the invention.